8 January 2011

Dynamic vs Static Rendering - by David Maletz

      Posted 01/08/11 07:10:00 pm  

Over the past decade, lightmapping and other precomputation methods have been used to simulate accurate lighting in games. Quake was the first computer game to use lightmapping, and the technique allowed the levels to have good lighting (for 1996) from many light sources with static shadows. Today, lightmapping is still used in many AAA game titles and can simulate accurate global illumination throughout levels, allowing game developers to have very photorealistic scenes. 

However, lightmapping and precomputation techniques come at the cost of flexible and dynamic capabilities. The complex lighting computed for lightmaps can take many minutes to compute, sometimes even hours depending on the level complexity and lightmapping settings. This computation, while very accurate, is fixed for the scene it was computed for. If the scene changes, the precomputed lightmap data is invalidated, and recomputing that data is often impractical, as lightmaps take so long to generate. In many games, this problem is overlooked in favor of improved quality of renderings. However current trends in game development call for more dynamic scenes with more complex lighting such as view-dependent specular reflections, which cannot be completely precomputed.

The perfect rendering algorithm that is flexible, can handle any kind of scene, and is high quality does not run in real time. As graphic cards become more powerful, however, those high quality and dynamic renderings become faster and faster as well. It is realistic to think that in ten years such renderings will be feasible in real time. For instance, one of my own research papers (of which my profile picture is a screenshot of) was a flexible, high quality multi-bounce global illumination solver for diffuse and low-specular scenes, and could fully converge within a few seconds. That is not exceptional timing either, as many global illumination papers are reporting times in the interactive to a few seconds range. While right now these algorithms are still too slow for games, the performance cost for these rendering algorithms goes down every year.

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